[[index-modules]]
= Index Modules

[partintro]
--

Index Modules are modules created per index and control all aspects related to
an index.

[float]
[[index-modules-settings]]
== Index Settings

Index level settings can be set per-index.  Settings may be:

_static_::

They can only be set at index creation time or on a
<<indices-open-close,closed index>>.

_dynamic_::

They can be changed on a live index using the
<<indices-update-settings,update-index-settings>> API.

WARNING: Changing static or dynamic index settings on a closed index could
result in incorrect settings that are impossible to rectify without deleting
and recreating the index.

[float]
=== Static index settings

Below is a list of all _static_ index settings that are not associated with any
specific index module:

`index.number_of_shards`::

    The number of primary shards that an index should have.  Defaults to 5.
    This setting can only be set at index creation time.  It cannot be
    changed on a closed index.

`index.shard.check_on_startup`::
+
--
experimental[] Whether or not shards should be checked for corruption before opening. When
corruption is detected, it will prevent the shard from being opened. Accepts:

`false`::

    (default) Don't check for corruption when opening a shard.

`checksum`::

    Check for physical corruption.

`true`::

    Check for both physical and logical corruption. This is much more
    expensive in terms of CPU and memory usage.

`fix`::

    Check for both physical and logical corruption.  Segments that were reported
    as corrupted will be automatically removed. This option *may result in data loss*.
    Use with extreme caution!

Checking shards may take a lot of time on large indices.
--

[[index-codec]] `index.codec`::

    experimental[] The +default+ value compresses stored data with LZ4
    compression, but this can be set to +best_compression+
    which uses https://en.wikipedia.org/wiki/DEFLATE[DEFLATE] for a higher
    compression ratio, at the expense of slower stored fields performance.

[float]
[[dynamic-index-settings]]
=== Dynamic index settings

Below is a list of all _dynamic_ index settings that are not associated with any
specific index module:


`index.number_of_replicas`::

    The number of replicas each primary shard has.  Defaults to 1.

`index.auto_expand_replicas`::

    Auto-expand the number of replicas based on the number of available nodes.
    Set to a dash delimited lower and upper bound (e.g. `0-5`) or use `all`
    for the upper bound (e.g. `0-all`).  Defaults to `false` (i.e. disabled).

`index.refresh_interval`::

    How often to perform a refresh operation, which makes recent changes to the
    index visible to search.  Defaults to `1s`.  Can be set to `-1` to disable
    refresh.

`index.max_result_window`::

    The maximum value of `from + size` for searches to this index. Defaults to
    `10000`. Search requests take heap memory and time proportional to
    `from + size` and this limits that memory. See
    {ref}/search-request-scroll.html[Scroll] for a more efficient alternative
    to raising this.

`index.blocks.read_only`::

    Set to `true` to make the index and index metadata read only, `false` to
    allow writes and metadata changes.

`index.blocks.read`::

    Set to `true` to disable read operations against the index.

`index.blocks.write`::

    Set to `true` to disable write operations against the index.

`index.blocks.metadata`::

    Set to `true` to disable index metadata reads and writes.

`index.ttl.disable_purge`::

    experimental[] Disables the purge of <<mapping-ttl-field,expired docs>> on
    the current index.


[float]
=== Settings in other index modules

Other index settings are available in index modules:

<<analysis,Analysis>>::

    Settings to define analyzers, tokenizers, token filters and character
    filters.

<<index-modules-allocation,Index shard allocation>>::

    Control over where, when, and how shards are allocated to nodes.

<<index-modules-mapper,Mapping>>::

    Enable or disable dynamic mapping for an index.

<<index-modules-similarity,Similarities>>::

    Configure custom similarity settings to customize how search results are
    scored.

<<index-modules-slowlog,Slowlog>>::

    Control over how slow queries and fetch requests are logged.

<<index-modules-store,Store>>::

    Configure the type of filesystem used to access shard data.

<<index-modules-translog,Translog>>::

    Control over the transaction log and background flush operations.

--

include::index-modules/analysis.asciidoc[]

include::index-modules/allocation.asciidoc[]

include::index-modules/mapper.asciidoc[]

include::index-modules/similarity.asciidoc[]

include::index-modules/slowlog.asciidoc[]

include::index-modules/store.asciidoc[]

include::index-modules/translog.asciidoc[]